1. Field of the Invention
Embodiments of the present invention generally relate to wireless devices and more specifically to receiving and transmitting signals between transceivers.
2. Description of the Related Art
Generally, a communication system includes a transmitter and receiver, which transmit and receive information signals over a transmission media such as wires or atmosphere. When atmosphere is used, the transmission is commonly referred to as “wireless communication.” Examples of various types of wireless communication systems include digital cellular, packet data paging, wireless local area networks (LAN), wireless wide area networks (WAN), personal communication systems and others.
The capacity of a wireless communication system (i.e. the number and density of users that can be serviced) is heavily influenced by co-channel interference (CCI). CCI interference from adjacent access points (APs) and nearby mobiles represents a fundamental issue in system design and deployment. CCI occurs when signals from two access points operating on the same frequency are within a distance that allows the signals to propagate from one AP within one basic service set (BSS) to another AP within another BSS. Because the two signals are on the same channel, each AP allows both signals to pass to its respective baseband processor.
Conventionally, mitigating co-channel interference has been achieved using frequency reuse planning, and other isolation techniques that rely on the wireless medium environment.
One method for mitigating co-channel interference involves increasing the number of frequency channels available for use. When more frequency channels are available, a larger physical distance can be provided between access points using the same channel. This method may work well for wireless networks having access to a large number of channels but not as well for those with a limited number of frequency channels. For example, a wireless network operating in an IEEE 802.11a environment having as many as twelve non-overlapping channels has a distinct advantage over a wireless environment operating in an IEEE 802.11b environment where the number of non-overlapping channels is limited to three. The number of non-overlapping channels available in a given band and a given geographic region depends on government regulations and is usually difficult or impossible to change.
Increasing the distance between each BSS operating on the same channel may be used to allow the propagation loss of the transmission medium to attenuate the interfering signals to low levels. Unfortunately, as access points become denser with the proliferation of wireless devices, distances between access points decrease and thereby increases the likelihood of CCI.
Generally in IEEE 802.11 networks all wireless devices are required to operate according to the distributed coordination function (DCF) rules. All wireless devices and access points operating under these rules must perform a clear channel assessment (CCA) before transmitting. The CCA may result in one BSS waiting for signals intended for another BSS. This is referred to as CCA capture. Due to CCA capture, the available channel capacities from two BSSs operating on the same frequency channel are shared between all of the wireless devices for both BSSs thereby degrading the overall BSS throughput.
Generally, within a single BSS, all wireless devices are usually able to hear one another. However, in the case of multiple BSSs separated by some distance and on the same channel, some wireless devices within one BSS may hear messages from the interfering BSS while others do not. Therefore, the co-channel interference may preoccupy some of the wireless receivers and therefore not allow them to communicate with their own BSS thereby reducing the BSS communication efficiency. This interference may occur even if the signal strength of the arriving signal is lower than the standard-defined CCA threshold. However, once receiving a packet, most devices will attempt to receive the complete packet independent of the signal strength, source, destination or network identification addresses. This is commonly referred to as receiver capture. Both CCA capture and receiver capture may cause the throughput to degrade for some or all of the devices in a BSS. In some circumstance not all devices in a BSS are able to hear co-channel interference. In this case, a device may begin transmission to another device that is already busy receiving a co-channel interference signal.
Therefore, what is needed is a method and apparatus to configure a plurality of; adjacent wireless network circuits to operate simultaneously without reducing communication system efficiency and without increasing cost and complexity.